Phased array antennas are a major part of today's military and commercial sensors and communication systems. In phased array antennas, multiple antennas are often configured together into an antenna array to form a directional radiation pattern. More advanced phased arrays use phase shifting techniques to scan their radiation patterns in space. A phased array usually comprises a number of dipole antenna elements, commonly spaced at a equal distance. Each element or sub array of elements are connected to a phase shifter followed by a summing node. Varying the frequency of operation can also be used in lieu of the phase shifters to form the radiation pattern.
Active phased arrays or active electronically scanned arrays (AESAs) include amplifiers at individual antenna elements or subarrays of the antenna array. Compared with passive phased arrays, active phased arrays provide greater sensitivity. In addition, AESAs are more reliable than mechanically scanned antennas. An active phased array system front end typically comprises antennas and Transmit/Receive (T/R) modules. A primary reoccurring cost of an active phased array system is for the T/R modules. The cost of the T/R modules stems from a number of high dollar components required for each T/R module, including switches, amplifiers, phase shifters, variable attenuators, etc., which are multiplied by the total number of T/R modules used in the array. When arrays can have hundreds or even thousands of elements and T/R modules, the number of components, their associated costs, and the dissipated power have a significant impact on the overall performance and cost of the array.
An active phased array's effective radiated power and overall RF system capability are determined largely by the array's transmitted RF power. Therefore, the T/R module and its amplifiers are designed to achieve as much transmitted power as possible. The transmitted power level may be increased by increasing the number of antenna elements and T/R modules in the system. However, phased arrays are typically restricted to a small footprint, reducing the spatial degrees of freedom available to enhance array performance. When the array is spatially contained, the power dissipated by the T/R module may become an increasingly important issue as the number of T/R modules increases. The available space and heat removal capability may limit the level of transmit power that an active phased array can realistically achieve.
Operating at RF and microwave frequencies, the T/R module usually employs Monolithic Microwave Integrated Circuit (MMIC) components to reduce the footprint. As the transmit power becomes greater, the output switch of the T/R module may become more costly and limiting in its performance. The higher the output power, the fewer switches on the market available capable of handling the output power, and the more costly they may become. Many amplifiers are available for use in a T/R module that can deliver more output power than can be handled by any conventional switch. Also, the signal losses through the conventional switch may be substantial enough to impact the transmitted power and the amount of power dissipated as heat. Thus, a low-cost output switch that is capable of transmitting high power level, while reducing power losses, is greatly desired.